System and method for common phase error and inter-carrier interference estimation and compensation

ABSTRACT

A system and method for transmitting an orthogonal frequency-division multiplexed signal with a group distributed phase tracking reference signal subcarrier structure, and for estimating, and compensating for, both common phase error, and inter-carrier interference.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a divisional application of U.S. patentapplication Ser. No. 15/880,419, filed Jan. 25, 2018, which claimspriority to and the benefit of U.S. Provisional Application No.62/541,035 filed Aug. 3, 2017, entitled “SYSTEM AND METHOD FOR PHASETRACKING REFERENCE SIGNAL (PTRS) STRUCTURE AND FREQUENCY DOMAIN PHASENOISE COMMON PHASE ERROR (CPE) AND INTER-CARRIER INTERFERENCE (ICI)COMPENSATION”. The entire contents of both of the applicationsidentified in this paragraph are incorporated herein by reference.

FIELD

One or more aspects of embodiments according to the present disclosurerelate to communication systems, and more particularly, to a system andmethod for common phase error and inter-carrier interference estimationand compensation.

BACKGROUND

Phase noise, caused by oscillator imperfections, affects theorthogonality of subcarriers in an orthogonal frequency-divisionmultiplexing (OFDM) system. The phase noise process may be random innature and for a phase-locked loop (PLL) based oscillator, iteffectively causes a rotation of time domain baseband samples of thein-phase and quadrature components (IQ samples) by a small amount, andthe randomness can be characterized by a power spectral density (PSD) inthe frequency domain. This leads to a common phase error (CPE), whichhas similar impact on each subcarrier, and inter-carrier interference(ICI), which may be different for each subcarrier and may causescattering of the received constellation points in OFDM based systems.The total power of CPE and ICI observed at the center tone may be theintegrated phase noise PN (IPN), which may also be obtained byintegrating the PSD of the PN process over the occupied bandwidth (BW).If the phase noise PSD is wide compared to the subcarrier spacing, moreof the total power of the phase noise (IPN) will be contributed as ICIinstead of as CPE. The phase noise may be particularly severe for highercarrier frequencies such as millimeter-wave frequency bands above 6 GHz.

A phase tracking reference signal (PTRS) has been introduced in the NewRadio (NR) standard, to enable compensation of oscillator phase noise.PTRS may be utilized at high carrier frequencies (such asmillimeter-wave) to mitigate phase noise. However, a fully distributedPTRS structure may be suitable only for CPE estimation and compensation,and may not be of use in mitigating ICI.

SUMMARY

Aspects of embodiments of the present disclosure are directed toward asystem and method for transmitting an orthogonal frequency-divisionmultiplexed signal with a group distributed phase tracking referencesignal subcarrier structure, and for estimating, and compensating for,both common phase error, and inter-carrier interference.

According to an embodiment of the present disclosure there is provided amethod, including: estimating a channel using demodulation referencesignal subcarriers from a received signal; estimating a common phaseerror term using the estimated channel and phase tracking referencesignal subcarriers; and estimating one or more inter-carrierinterference terms, including: canceling, from the received signal, theestimated common phase error term to form a first compensated receivedsignal; and estimating, based on the first compensated received signal,a first inter-carrier interference term.

In one embodiment, the method further includes calculating a value ofthe transmitted signal in a subcarrier using known PTRS pilots.

In one embodiment, the estimating of the inter-carrier interferenceterms further includes: iteratively, for a range of values of an integeri greater than 1 and less than a set integer L: canceling, from areceived signal, the estimated common phase error, and the first through(i−1)-th inter-carrier interference terms, to form an i-th compensatedreceived signal; and estimating, using the i-th compensated receivedsignal, an i-th inter-carrier interference term.

In one embodiment, the estimating of the common phase error includescalculating a phase of the estimated common phase error according to

Ĵ[0]=

((Ĥ[

]X[

])^(H)Y[

]), wherein:

is a set of phase tracking reference signal subcarriers; [

] is a diagonal matrix the p-th diagonal element of which is equal tothe estimated channel response for the p-th subcarrier from among theset

; X[

] is the transmitted signal in subcarriers from among the set

; Y[

] is the received signal in subcarriers from among the set

; and H as a superscript denotes a conjugate transpose.

In one embodiment, the estimating of the common phase error furtherincludes setting an amplitude of the estimated common phase error to beequal to 1.

In one embodiment, the phase tracking reference signal subcarriersinclude N_(c)N_(PTRS) subcarriers, arranged in N_(c) groups, each of theN_(c) groups including N_(PTRS) adjacent subcarriers.

In one embodiment, the canceling, from the received signal, theestimated common phase error, and the first through (i−1)-thinter-carrier interference terms, to form the i-th compensated receivedsignal, includes calculating the i-th compensated received signalY_(SIC)[

_(ii)] according to

Y _(SIC)[

_(ii)]=Y[

_(ii)]−Ĵ[0]Ĥ[

_(ii)]X[

_(ii)], for i=1, and

[

_(ii)]=Y[

_(ii)]−Ĵ[0]Ĥ[

_(ii)]X[

_(ii)]−Ĵ[1]Ĥ[

_((i−1)(i+1))]X[

_((i−1)(i+))]−Ĵ[−1]Ĥ[

_((i+1)(i−1))]X[

_((i+1)(i−1))]− . . . −Ĵ[i−1]Ĥ[

_(1(2i−1))]X[

_(1(2i−1))]−Ĵ[−(i−1)]Ĥ[

_((2i−1)1)]X[

_((2i−1)1)],for i>1 wherein:

_(ij)={k_(1(i+1)), . . . , k_(1(N) _(PTRS) _(−j)), . . . , k_(N) _(c)_((i+1)), . . . , k_(N) _(PTRS) _(−j))}, wherein k_(pq) is the q-thsubcarrier of the p-th group of subcarriers of the phase trackingreference signal subcarriers; Ĥ[

_(ij)] is a diagonal matrix the p-th diagonal element of which is equalto the estimated channel response for the p-th subcarrier from among theset

_(ij); X[

_(pq)] is the transmitted signal in subcarriers from among the set

_(pq) Y[

_(U)] is the received signal in subcarriers from among the set

_(ii); Ĵ[0] is the estimated common phase error; and Ĵ[p], for p notequal to zero, is the estimated p-th inter-carrier interference term.

In one embodiment, the estimating, based on the i-th compensatedreceived signal, of the i-th inter-carrier interference term includescalculating the i-th estimated inter-carrier interference term Ĵ[i]according to

${\begin{bmatrix}{{Re}\left\{ {\hat{J}\lbrack i\rbrack} \right\}} \\{{Im}\left\{ {\hat{J}\lbrack i\rbrack} \right\}}\end{bmatrix}_{2 \times 1} = {\left( {T^{H}T} \right)^{- 1}{T^{H}\begin{bmatrix}{{Re}\left\{ {Y_{SIC}\left\lbrack \kappa_{ii} \right\rbrack} \right\}} \\{{Im}\left\{ {Y_{SIC}\left\lbrack \kappa_{ii} \right\rbrack} \right\}}\end{bmatrix}}_{2{({N_{c}{({N_{PTRS} - {2i}})}})} \times 1}}},$

${{{wherein}\text{:}\mspace{14mu} T} = \begin{bmatrix}A_{{({N_{c}{({N_{PTRS} - {2i}})}})} \times 1} & B_{{({N_{c}{({N_{PTRS} - {2i}})}})} \times 1} \\C_{{({N_{c}{({N_{PTRS} - {2i}})}})} \times 1} & D_{{({N_{c}{({N_{PTRS} - {2i}})}})} \times 1}\end{bmatrix}_{2{({N_{c}{({N_{PTRS} - {2i}})}})} \times 2}};$  A = Re{Ĥ[κ_(0(2i))]X[κ_(0(2i))]} − Re{Ĥ[κ_((2i)0)]X[κ_((2i)0)]};  B = −Im{Ĥ[κ_(0(2i))]X[κ_(0(2i))]} − Im{Ĥ[κ_((2i)0)]X[κ_((2i)0)]};  C = Im{Ĥ[κ_(0(2i))]X[κ_(0(2i))]} − Im{Ĥ[κ_((2i)0)]X[κ_((2i)0)]}; and  D = Re{Ĥ[κ_(0(2i))]X[κ_(0(2i))]} + Re{Ĥ[κ_((2i)0)]X[κ_((2i)0)}}.

In one embodiment, the method further includes calculating a finalcompensated received signal Y_(ICI comp)[l] based on a matched filter,wherein an order of the filter is dependent on a number of estimatedinter-carrier interference terms.

According to an embodiment of the present disclosure there is provided amethod, including: estimating a channel using demodulation referencesignal subcarriers from a received signal; estimating a common phaseerror term using the estimated channel and phase tracking referencesignal subcarriers; and estimating one or more inter-carrierinterference terms, including: canceling, from the received signal, theestimated common phase error term to form a first compensated receivedsignal; and jointly estimating, based on the first compensated receivedsignal, L inter-carrier interference terms, L being a set integergreater than 0.

In one embodiment, the method further includes calculating a value ofthe transmitted signal in a subcarrier using known PTRS pilots.

In one embodiment, the estimating of the common phase error includescalculating a phase of the estimated common phase error according to

Ĵ[0]=

((H[

]X[

])^(H)Y[

]), wherein:

is a set of phase tracking reference signal subcarriers; Ĥ[

] is a diagonal matrix the p-th diagonal element of which is equal tothe estimated channel response for the p-th subcarrier from among theset

; X[

] is the transmitted signal in subcarriers from among the set

; Y[

] is the received signal in subcarriers from among the set

; and H as a superscript denotes a conjugate transpose.

In one embodiment, the estimating of the common phase error furtherincludes setting an amplitude of the common phase error to be equal to1.

In one embodiment, the phase tracking reference signal subcarriersinclude N_(c)N_(PTRS) subcarriers, arranged in N_(c) groups, each of theN_(c) groups including N_(PTRS) adjacent subcarriers.

In one embodiment, the canceling, from the received signal, theestimated common phase error to form a first compensated received signalincludes calculating the first compensated received signal Y_(CPEcomp)[

_(LL)] according to Y_(CPEcomp)[

_(LL)]=Y[

_(LL)]−Ĵ[0]Ĥ[

_(LL)]X[

_(LL)] wherein:

_(ij)={k_(1(i+1)), . . . , k_(1(N) _(PTRS) _(−j)), . . . , k_(N) _(c)_((i+1)), . . . , k_(N) _(PTRS) _(−j))} wherein k_(pq) is the q-th,subcarrier of the p-th group of subcarriers of the phase trackingreference signal subcarriers; Ĥ[

_(LL)] is a diagonal matrix the p-th diagonal element of which is equalto the estimated channel response for the p-th sub carrier from amongthe set

_(LL); X[

_(LL)] is the transmitted signal in subcarriers from among the set

_(LL); Y[

_(LL)] is the received signal in subcarriers from among the set

_(LL); and Ĵ[0] is the estimated common phase error.

In one embodiment, the jointly estimating, based on the firstcompensated received signal, of L inter-carrier interference terms,includes calculating the L estimated inter-carrier interference terms Ĵaccording to

${\begin{bmatrix}{{Re}\left\{ \hat{J} \right\}} \\{{Im}\left\{ \hat{J} \right\}}\end{bmatrix}_{2L \times 1} = {\left( {T^{H}T} \right)^{- 1}{T^{H}\begin{bmatrix}{{Re}\left\{ {Y_{CPEcomp}\left\lbrack \kappa_{LL} \right\rbrack} \right\}} \\{{Im}\left\{ {Y_{CPEcomp}\left\lbrack \kappa_{LL} \right\rbrack} \right\}}\end{bmatrix}}_{2{({N_{c}{({N_{PTRS} - {2L}})}})} \times 1}}},{{wherein}\text{:}}$${T = \begin{bmatrix}A_{{({N_{c}{({N_{PTRS} - {2L}})}})} \times L} & B_{{({N_{c}{({N_{PTRS} - {2L}})}})} \times L} \\C_{{({N_{c}{({N_{PTRS} - {2L}})}})} \times L} & D_{{({N_{c}{({N_{PTRS} - {2L}})}})} \times L}\end{bmatrix}_{2{({N_{c}{({N_{PTRS} - {2L}})}})} \times 2L}};$

andthe respective i-th columns A_(i), B_(i), C_(i), and D_(i) of A, B, C,and D are:

A _(i)=Re{Ĥ[

_((L−1)(L+1))]X[

_((L−1)(L+1))]}−Re{Ĥ[

_((L+1)(L−1))]X[

_((L+1)(L−1))]};

B _(i)=−Im{Ĥ[

_((L−1)(L+1))]X[

_((L−1)(L+1))]}−Im{Ĥ[

_((L+1)(L−1))]X[

_((L+1)(L−1))]};

C _(i)=Im{Ĥ[

_((L−1)(L+1))]X[

_((L−1)(L+1))]}−Im{Ĥ[

_((L+1)(L−1))]X[

_((L+1)(L−1))]}; and

D _(i)=Re{Ĥ[

_((L−1)(L+1))]X[

_((L−1)(L+1))]}+Re{Ĥ[

_((L+1)(L−1))]X[

_((L+1)(L−1))]}.

In one embodiment, the method further includes calculating a finalcompensated received signal Y_(ICI comp)[l] according toY_(ICI comp)[l]=Ĵ*[0]Y[l]+Ĵ*[1]Y[l+1]+Ĵ*[−1]Y[l−1]+ . . .+Ĵ*[L]Y[l+L]+Ĵ*[−L]Y[l−L].

According to an embodiment of the present disclosure there is provided aplurality of phase tracking reference signal subcarriers, the methodincluding transmitting the orthogonal frequency-division multiplexedsignal, wherein the phase tracking reference signal subcarriers are in aplurality of subcarriers, arranged in N_(c) groups, each of the N_(c)groups including a plurality of adjacent subcarriers.

In one embodiment, each group includes exactly N_(PTRS) adjacent phasetracking reference signal subcarriers, N_(PTRS) being an integer greaterthan 0.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present disclosure willbe appreciated and understood with reference to the specification,claims, and appended drawings wherein:

FIG. 1A is a time-frequency diagram of a phase tracking reference signalstructure, according to an embodiment of the present disclosure;

FIG. 1B is a time-frequency diagram of a phase tracking reference signalstructure, according to an embodiment of the present disclosure;

FIG. 2 is a flowchart of a method for estimating common phase error andinter-carrier interference, according to an embodiment of the presentdisclosure;

FIG. 3 is a flowchart of a method for estimating common phase error andinter-carrier interference, according to an embodiment of the presentdisclosure;

FIG. 4A is a block diagram of a transmitter and a receiver, according toan embodiment of the present disclosure;

FIG. 4B is a block diagram of a system for estimating, and compensatingfor, common phase error and inter-carrier interference, according to anembodiment of the present disclosure;

FIG. 5 is a graph of simulated performance, according to an embodimentof the present disclosure;

FIG. 6 is a graph of simulated performance, according to an embodimentof the present disclosure;

FIG. 7 is a graph of simulated performance, according to an embodimentof the present disclosure; and

FIG. 8 is a graph of simulated performance, according to an embodimentof the present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of asystem and method for common phase error and inter-carrier interferenceestimation and compensation provided in accordance with the presentdisclosure and is not intended to represent the only forms in which thepresent disclosure may be constructed or utilized. The description setsforth the features of the present disclosure in connection with theillustrated embodiments. It is to be understood, however, that the sameor equivalent functions and structures may be accomplished by differentembodiments that are also intended to be encompassed within the spiritand scope of the disclosure. As denoted elsewhere herein, like elementnumbers are intended to indicate like elements or features.

An OFDM transmission structure may include a plurality of uniformlyspaced subcarriers, e.g., 1024 subcarriers, separated by 15 kHz fromeach other. Of these subcarriers, a subset, e.g., 600 subcarriers, maybe used to transmit data and PTRS subcarriers; this subset may bereferred to as the resource block (RB) allocation. The remainder of thesubcarriers may be reserved for other purposes such as guard bands. Eachsubcarrier may be numbered with an index. For example, the subcarriersmay be given consecutive numbers beginning with 1 for thelowest-frequency subcarrier or beginning with 1 for thehighest-frequency subcarrier in the resource block allocation. Thecenter of the frequency range spanned by the plurality of subcarriersmay be at microwave or millimeter-wave frequencies, e.g., at 40 GHz orat 60 GHz. Each subcarrier may be independently modulated, e.g., using8×8 quadrature amplitude modulation (64 QAM) for data subcarriers, andusing quadrature phase shift keying (QPSK) modulation for the PTRSsubcarriers. Each subcarrier may transmit a stream of symbols (eachcorresponding to an interval of time). The length of the symbol intervalmay be selected to be the reciprocal of the spacing between subcarriers(e.g., the symbol interval may be selected to be 1/15,000 seconds) sothat each of the subcarriers is orthogonal to all of the othersubcarriers during each symbol interval. The New Radio standard usesOFDM.

The frequency domain received signal in the presence of phase noise ineach OFDM symbol may be represented as:

$\begin{matrix}\begin{matrix}{{Y\lbrack l\rbrack} = {{\sum\limits_{k = 0}^{N - 1}{{H\lbrack k\rbrack}{X\lbrack k\rbrack}{J\left\lbrack {l - k} \right\rbrack}}} + {Z\lbrack l\rbrack}}} \\{= {{{H\lbrack l\rbrack}{X\lbrack l\rbrack}{J\lbrack 0\rbrack}} + {\sum\limits_{{k = 0},{k \neq l}}^{N - 1}{{H\lbrack k\rbrack}{X\lbrack k\rbrack}\underset{\underset{ICI}{}}{J\left\lbrack {l - k} \right\rbrack}}} + {Z\lbrack l\rbrack}}}\end{matrix} & (1) \\{where} & \; \\{{{J\lbrack k\rbrack} = {\frac{1}{N}{\sum\limits_{n = 0}^{N - 1}{e^{j\; \theta_{n}}e^{{- j}\; 2\pi \; {{kn}/N}}}}}},} & (2)\end{matrix}$

Y[l] is the received signal at subcarrier l,

X[k] is the transmitted signal at subcarrier k,

Z[l] is white Gaussian noise,

H[k] is the channel at subcarrier k,

J[k] is the k-th term of inter-carrier interference,

N is the FFT size, and

θ_(n) is the phase noise realization at time sample n.

In equation 1, J[0] is the common phase error, and, as shown in Equation1, J[l−k] is inter-carrier interference. The channel at subcarrier k,(i.e., the transfer function of the channel, at the center frequency ofsubcarrier k) may be estimated using a demodulation reference signal(DMRS) that may be transmitted along with data and the PTRS subcarriers.

If θ_(n) is small, the following property may hold for inter-carrierinterference terms: J[k]=−J*[−k]

The PTRS structure, i.e., the set of subcarriers used to transmit thePTRS signals, may affect the ability of a receiver to performinterference cancellation, e.g., in particular, the ability of areceiver to compensate for inter-carrier interference. Accordingly, insome embodiments a group distributed structure is used. This structureis shown in FIGS. 1A and 1B, in one embodiment. The subcarriers withinthe resource block allocation are grouped into N_(c) groups of adjacentsubcarriers; these groups may be referred to as “chunks”. Each chunkincludes N_(PTRS) adjacent PTRS subcarriers. FIG. 1A is a time-frequencydiagram of a phase tracking reference signal structure, according to anembodiment of the present disclosure. FIG. 1A shows the grouping ofsubcarriers into chunks 110 and the allocation, within each chunk, toPTRS signals, of a set 120 of N_(PTRS) adjacent subcarriers. The set ofindexes of these carriers may be given by:

={k ₁₁ , . . . ,k _(1N) _(PTRS) , . . . ,k _(N) _(c) ₁ , . . . ,k _(N)_(c) _(N) _(PTRS) }

where k_(pq) is the q-th subcarrier of the p-th group of subcarriers ofthe PTRS subcarriers. FIG. 1B is a time-frequency diagram of a phasetracking reference signal structure, according to an embodiment of thepresent disclosure. FIG. 1B shows this numbering convention for the set120 of PTRS subcarriers in one of the chunks 110, chunk 1.

When the transmitted data include a group distributed PTRS structure,inter-carrier interference estimation and common phase error estimationand compensation may be performed according to two alternate methods,one of which is referred to herein as successive interferencecancellation (SIC) and the other of which is referred to as jointestimation of inter-carrier interference.

FIG. 2 is a flowchart of a method for estimating common phase error andinter-carrier interference, according to an embodiment of the presentdisclosure. Referring to FIG. 2, to perform inter-carrier interferenceestimation and common phase error estimation and compensation usingsuccessive interference cancellation, the following approach may beused. In general, the common phase error J[0] may not be precisely unitamplitude, but when the noise samples are small, the amplitude of J[0]may be approximately 1. Accordingly, the estimate Ĵ[0] of the commonphase error may be written:

Ĵ[0]=

,

and its estimated phase may be calculated, at 205, according to:

Ĵ[0]=

((Ĥ[

]X[

])^(H) Y[

])

where

is the set of phase tracking reference signal subcarriers,

H[κ] is a diagonal matrix the p-th diagonal element of which is equal tothe estimated channel response for the p-th subcarrier from among theset κ,

X[κ] is the transmitted signal in subcarriers from among the set κ,

Y[κ] is the received signal in subcarriers from among the set κ, and

H as a superscript denotes a conjugate transpose.

Next, a set of L inter-carrier interference terms may be iterativelyestimated, in a loop including 210 through 235. The value of L providingacceptable performance may depend on N_(PTRS), on N_(c), and on thephase noise characteristics. L may be selected offline (e.g., usingsimulations to identify a value that provides good performance that isrelatively insensitive to the phase noise characteristics) and stored ina buffer. At 210, the loop index i is initialized to 1. At 215, a set ofPTRS subcarriers suitable for estimating the i-th inter-carrierinterference term is selected. This may be done by defining thefollowing set:

_(ij) ={k _(1(i+1)) , . . . ,k _(1(N) _(PTRS) _(−j)) , . . . ,k _(N)_(c) _((i+1)) , . . . ,k _(N) _(PTRS) _(−j))}

and selecting the set κ_(ii) as the set of PTRS subcarriers to be usedfor estimating i-th inter-carrier interference term.

At 220, the estimated common phase error, and the first through (i−1)-thinter-carrier interference terms may be canceled from the receivedsignal according to:

Y _(SIC)[

_(ii)]=Y[

_(ii)]−Ĵ[0]Ĥ[

_(ii)]X[

_(ii)], for i=1, and

[

_(ii)]=Y[

_(ii)]−Ĵ[0]Ĥ[

_(ii)]X[

_(ii)]−Ĵ[1]Ĥ[

_((i−1)(i+1))]X[

_((i−1)(i+))]−Ĵ[−1]Ĥ[

_((i+1)(i−1))]X[

_((i+1)(i−1))]− . . . −Ĵ[i−1]Ĥ[

_(1(2i−1))]X[

_(1(2i−1))]−Ĵ[−(i−1)]Ĥ[

_((2i−1)1)]X[

_((2i−1)1)],for i>1

where

_(ij)={k_(1(i+1)), . . . , k_(1(N) _(PTRS) _(−j)), . . . , k_(N) _(c)_((i+1)), . . . , k_(N) _(PTRS) _(−j))}, wherein k_(pq) is the q-thsubcarrier of the p-th group of subcarriers of the phase trackingreference signal subcarriers),

Ĥ[

_(ij)] is a diagonal matrix the p-th diagonal element of which is equalto the estimated channel response for the p-th subcarrier from among theset

_(ij),

X[

_(pq)] is the transmitted signal in subcarriers from among the set

_(pq),

Y[

_(ii)] is the received signal in subcarriers from among the set

_(ii),

Ĵ[0] is the estimated common phase error, and

Ĵ[p], for p not equal to zero, is the estimated p-th inter-carrierinterference term.

The result, Y_(SIC)[

_(ii)], may be referred to as the i-th compensated received signal.

The next (i-th) inter-carrier interference term may then be estimated,at 225, based on the i-th compensated received signal, according to:

${\begin{bmatrix}{{Re}\left\{ {\hat{J}\lbrack i\rbrack} \right\}} \\{{Im}\left\{ {\hat{J}\lbrack i\rbrack} \right\}}\end{bmatrix}_{2 \times 1} = {\left( {T^{H}T} \right)^{- 1}{T^{H}\begin{bmatrix}{{Re}\left\{ {Y_{SIC}\left\lbrack \kappa_{ii} \right\rbrack} \right\}} \\{{Im}\left\{ {Y_{SIC}\left\lbrack \kappa_{ii} \right\rbrack} \right\}}\end{bmatrix}}_{2{({N_{c}{({N_{PTRS} - {2i}})}})} \times 1}}},{where}$${T = \begin{bmatrix}A_{{({N_{c}{({N_{PTRS} - {2i}})}})} \times 1} & B_{{({N_{c}{({N_{PTRS} - {2i}})}})} \times 1} \\C_{{({N_{c}{({N_{PTRS} - {2i}})}})} \times 1} & D_{{({N_{c}{({N_{PTRS} - {2i}})}})} \times 1}\end{bmatrix}_{2{({N_{c}{({N_{PTRS} - {2i}})}})} \times 2}},{A = {{{Re}\left\{ {{\hat{H}\left\lbrack \kappa_{0{({2i})}} \right\rbrack}{X\left\lbrack \kappa_{0{({2i})}} \right\rbrack}} \right\}} - {{Re}\left\{ {{\hat{H}\left\lbrack \kappa_{{({2i})}0} \right\rbrack}{X\left\lbrack \kappa_{{({2i})}0} \right\rbrack}} \right\}}}},{{B = {{{- {Im}}\left\{ {{\hat{H}\left\lbrack \kappa_{0{({2i})}} \right\rbrack}{X\left\lbrack \kappa_{0{({2i})}} \right\rbrack}} \right\}} - {{Im}\left\{ {{\hat{H}\left\lbrack \kappa_{{({2i})}0} \right\rbrack}{X\left\lbrack \kappa_{{({2i})}0} \right\rbrack}} \right\}}}};}$C = Im{Ĥ[κ_(0(2i))]X[κ_(0(2i))]} − Im{Ĥ[κ_((2i)0)]X[κ_((2i)0)]}, andD = Re{Ĥ[κ_(0(2i))]X[κ_(0(2i))]} + Re{Ĥ[κ_((2i)0)]X[κ_((2i)0)}}.

The index i may then be incremented (at 230) and compared to the looplimit L (at 235), and the loop may repeat until i exceeds L.

The estimated common phase error and inter-carrier interference termsmay then be used to calculate a final compensated received signalY_(ICI comp)[l] according to:

Y _(ICI comp)[l]=Ĵ* [0]Y[l]+Ĵ*[1]Y[l+1]+Ĵ*[−1]Y[l−1]+ . . .+Ĵ*[L]Y[l+L]+Ĵ*[−L]Y[l−L].

The above expression may be seen to be a finite impulse response (FIR)filter.

FIG. 3 is a flowchart of a method for estimating common phase error andinter-carrier interference, according to an embodiment of the presentdisclosure. Referring to FIG. 3, to perform inter-carrier interferenceestimation and common phase error estimation and compensation usingjoint estimation of inter-carrier interference, the following approachmay be used. The estimate j[0] of the common phase error may becalculated, at 305, in the same manner as described above, for the caseof inter-carrier interference estimation and common phase errorestimation and compensation using successive interference cancellation,i.e., writing

Ĵ[0]=

and calculating the estimated phase according to:

Ĵ[0]=

((Ĥ[

]X[

])^(H) Y[

]).

At 310, a set of PTRS subcarriers suitable for jointly estimating the Linter-carrier interference terms is selected. This may be done byselecting the set

_(LL) as the set of PTRS subcarriers to be used for jointly estimatingthe L inter-carrier interference terms. At 315, the common phase errormay then be canceled according to

Y _(CPEcomp)[

_(LL)]=Y[

_(LL)]−Ĵ[0]Ĥ[

_(LL)]X[

_(LL)]

where

_(ij)={k_(1(i+1)), . . . , k_(1(N) _(PTRS) _(−j)), . . . , k_(N) _(c)_((i+1)), . . . , k_(N) _(PTRS) _(−j))} (where k_(pq) is the q-thsubcarrier of the p^(th) group of subcarriers of the phase trackingreference signal subcarriers),

Ĥ[

_(LL)] is a diagonal matrix the p^(th) diagonal element of which isequal to the estimated channel response for the p^(t) subcarrier fromamong the set

_(LL),

X[

_(LL)] is the transmitted signal in subcarriers from among the set

_(LL),

Y[

_(LL)] is the received signal in subcarriers from among the set

_(LL), and

Ĵ[0] is the estimated common phase error.

At 320, the L inter-carrier interference terms may then be estimatedjointly according to

${\begin{bmatrix}{{Re}\left\{ \hat{J} \right\}} \\{{Im}\left\{ \hat{J} \right\}}\end{bmatrix}_{2L \times 1} = {\left( {T^{H}T} \right)^{- 1}{T^{H}\begin{bmatrix}{{Re}\left\{ {Y_{CPEcomp}\left\lbrack \kappa_{LL} \right\rbrack} \right\}} \\{{Im}\left\{ {Y_{CPEcomp}\left\lbrack \kappa_{LL} \right\rbrack} \right\}}\end{bmatrix}}_{2{({N_{c}{({N_{PTRS} - {2L}})}})} \times 1}}},{where}$${T = \begin{bmatrix}A_{{({N_{c}{({N_{PTRS} - {2L}})}})} \times L} & B_{{({N_{c}{({N_{PTRS} - {2L}})}})} \times L} \\C_{{({N_{c}{({N_{PTRS} - {2L}})}})} \times L} & D_{{({N_{c}{({N_{PTRS} - {2L}})}})} \times L}\end{bmatrix}_{2{({N_{c}{({N_{PTRS} - {2L}})}})} \times 2L}},$

and

the respective i-th columns A_(i), B_(i), C_(i), and D_(i) of A, B, C,and D are:

A _(i)=Re{Ĥ[

_((L−1)(L+1))]X[

_((L−1)(L+1))]}−Re{Ĥ[

_((L+1)(L−1))]X[

_((L+1)(L−1))]};

B _(i)=−Im{Ĥ[

_((L−1)(L+1))]X[

_((L−1)(L+1))]}−Im{Ĥ[

_((L+1)(L−1))]X[

_((L+1)(L−1))]};

C _(i)=Im{Ĥ[

_((L−1)(L+1))]X[

_((L−1)(L+1))]}−Im{Ĥ[

_((L+1)(L−1))]X[

_((L+1)(L−1))]}; and

D _(i)=Re{Ĥ[

_((L−1)(L+1))]X[

_((L−1)(L+1))]}+Re{Ĥ[

_((L+1)(L−1))]X[

_((L+1)(L−1))]}.

The estimated common phase error and inter-carrier interference termsmay then be used to calculate, in the same manner as described above(for the case of inter-carrier interference estimation and common phaseerror estimation and compensation using successive interferencecancellation) a final compensated received signal Y_(ICI comp)[l], i.e.,according to

Y _(ICI comp)[l]=Ĵ* [0]Y[l]+Ĵ*[1]Y[l+1]+Ĵ*[−1]Y[l−1]+ . . .+Ĵ*[L]Y[l+L]+Ĵ*[−L]Y[l−L].

FIG. 4A is a block diagram of a transmitter 405 and a receiver 410,according to an embodiment of the present disclosure. FIG. 4A shows ablock diagram of a transmitter (which may transmit a PTRS structureaccording to an embodiment of the present disclosure) and a receiver(which may employ a system and method, according to an embodiment of thepresent disclosure, for estimating, and compensating for, both commonphase error, and inter-carrier interference). FIG. 4B is a block diagramof a system for estimating, and compensating for, common phase error andinter-carrier interference, according to an embodiment of the presentdisclosure. FIG. 4B shows a block diagram for two embodiments, one ofwhich employs successive interference cancellation (SIC) and the otherof which employs joint estimation of inter-carrier interference. PTRSsubcarriers are extracted from a frequency-domain signal (the output ofthe FFT 415) by a PTRS subcarrier extractor 420, and the transmittedPTRS signal (X[

_(pq)]) is generated in the PTRS symbol generator 425 using the knownPTRS pilots. Common phase error and inter-carrier interference terms areestimated by the CPE and ICI terms estimator 430 and buffered in thebuffer 435 of CPE and ICI terms. The CPE and ICI terms estimatorreceives the estimated channel response (Ĥ[k]) from the channelestimator 440, which estimates the response of each channel usingdemodulation reference signals (DMRSs) received from the DMRSsubcarriers extractor 445. The dashed arrow 450, indicating a flow ofinformation from the buffer of CPE and ICI terms back to the CPE and ICIterms estimator, is used (i.e., the information flow is present) in theembodiment employing successive interference cancellation and absentfrom the embodiment employing joint estimation of inter-carrierinterference. Once the common phase error and inter-carrier interferenceterms have been estimated, the final compensated received signalY_(ICI comp)[l] is calculated by the CPE and ICI compensator 455, theoutput of which is fed (along with the output of the channel estimator)to the detector 460 (the output of which is fed to the decoder 465).Each of the blocks in FIG. 4B, except the Rx (receive) filter 470, maybe a separate processing circuit (discussed in further detail below), oreach of these blocks may (equivalently) be implemented as a separateportion of a single processing circuit, or some or all of them may beimplemented in hardware or firmware executed by a processing circuitthat is configured to operate as a stored-program computer.

The term “processing circuit” is used herein to mean any combination ofhardware, firmware, and software, employed to process data or digitalsignals. Processing circuit hardware may include, for example,application specific integrated circuits (ASICs), general purpose orspecial purpose central processing units (CPUs), digital signalprocessors (DSPs), graphics processing units (GPUs), and programmablelogic devices such as field programmable gate arrays (FPGAs). In aprocessing circuit, as used herein, each function is performed either byhardware configured, i.e., hard-wired, to perform that function, or bymore general purpose hardware, such as a CPU, configured to executeinstructions stored in a non-transitory storage medium. A processingcircuit may be fabricated on a single printed circuit board (PCB) ordistributed over several interconnected PCBs. A processing circuit maycontain other processing circuits; for example a processing circuit mayinclude two processing circuits, an FPGA and a CPU, interconnected on aPCB.

Each of FIGS. 5-8 is a graph of simulated performance, according to anembodiment of the present disclosure. FIGS. 5-8 show simulatedperformance for various embodiments. The simulations illustrate thatsignificant improvements in performance are possible, using common phaseerror and inter-carrier interference compensation according toembodiments of the present disclosure.

FIGS. 5 and 6 use simulations in which the effective code rate is fixed,and FIGS. 7 and 8 use simulations in which the transmit block size isfixed. FIGS. 5 and 7 use simulations in which successive interferencecancellation is employed, and FIGS. 6 and 8 use simulations in whichjoint estimation of inter-carrier interference is employed. Each of thegraphs of FIGS. 5-8 shows a plurality of curves, numbered in order. Thefirst curve in each of FIGS. 5 and 6 (i.e., each of curves 501 and 601)shows the results for a simulation in which no compensation isperformed. The eighth curves in FIGS. 5 and 6 (i.e., curves 508 and 608)show the results for a simulation in which “genie” compensation isperformed, i.e., in which the true common phase error and inter-carrierinterference (which are known within the simulation) are used in thecompensation. The second through seventh curves in FIGS. 5 and 6 showthe results for simulations in which k is 50, 25, 10, 5, 2, and 1,respectively. The first seven curves of each of FIGS. 5 and 6 have 1resource element (RE) per resource block (RB), 1 RE per 1 RB, 2 REs per2 RBs, 5 REs per 5 RBs, 10 REs per 10 RBs, 25 REs per 25 RBs, and 50 REsper 50 RBs, respectively.

In FIG. 7, in curves 701-707, the numbers of PTRS subcarriers are 0, 5,10, 25, 25, 50, and 50, respectively, and the numbers of chunks are 0,5, 10, 25, 1, 50, 2, respectively. Curves 701, 702, and 703 show theresults for simulations in which no compensation is used. Compensationis used in the simulations for curves 704-707, with curves 704 and 706having common phase error compensation only, and curves 705 and 707 alsohaving compensation for 3 and 6 inter-carrier interference terms,respectively. In FIG. 8, in curves 801-805, the numbers of PTRSsubcarriers are 0, 5, 10, 25, and 25, respectively, and the numbers ofchunks are 0, 5, 10, 25, and 1, respectively. Curves 801 and 802 showthe results for simulations in which no compensation is used.Compensation is used in the simulations for curves 803-805, with curves803 and 804 having common phase error compensation only, and curve 805also having compensation for 4 inter-carrier interference terms.

In light of the foregoing, some embodiments include a group distributedPTRS structure to be able to perform inter-carrier interferenceestimation and compensation. Moreover, because the fully distributedPTRS structure with N_(PTRS)=1 is a special case of a group distributedPTRS structure, there may be little or no impact to implementationswhere only CPE is mitigated. The group distributed PTRS structure maymake it possible to handle those phase noise models with wide PSDrelative to the subcarrier spacing. The group distributed PTRS structuremay also have an advantage over a fully localized PTRS structure whichmay suffer from a deep fading problem if the allocated PTRS subcarriersare experiencing a poor quality channel condition. Some embodimentsfurther provide a frequency domain successive interference cancellationmethod and joint method for inter-carrier interference estimation, and afrequency domain FIR filter for inter-carrier interference compensationthat may improve the performance significantly compared to common phaseerror compensation only.

As used herein, calculating a first value “based on” a second valuemeans calculating the first value as the output of a function the inputto which includes the second value. As used herein “canceling” anestimated error from a signal, or “compensating” a signal for an error,means making a correction to a signal based on the estimated error; thisneed not result in entirely eliminating, from the signal, the effect ofthe error. As used herein, two subcarriers are “adjacent” if there areno other subcarriers between them in frequency. A group of carriers isreferred to as a group of “adjacent subcarriers” if, for every twocarriers in the group there are no subcarriers, not in the group,between the two carriers in frequency.

It will be understood that, although the terms “first”, “second”,“third”, etc., may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, a first element, component, region, layer or sectiondiscussed herein could be termed a second element, component, region,layer or section, without departing from the spirit and scope of theinventive concept.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the inventiveconcept. As used herein, the terms “substantially,” “about,” and similarterms are used as terms of approximation and not as terms of degree, andare intended to account for the inherent deviations in measured orcalculated values that would be recognized by those of ordinary skill inthe art. As used herein, the term “major component” refers to acomponent that is present in a composition, polymer, or product in anamount greater than an amount of any other single component in thecomposition or product. In contrast, the term “primary component” refersto a component that makes up at least 50% by weight or more of thecomposition, polymer, or product. As used herein, the term “majorportion”, when applied to a plurality of items, means at least half ofthe items.

As used herein, the singular forms “a” and “an” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising”, when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. Expressions such as “at least one of,” when preceding alist of elements, modify the entire list of elements and do not modifythe individual elements of the list. Further, the use of “may” whendescribing embodiments of the inventive concept refers to “one or moreembodiments of the present disclosure”. Also, the term “exemplary” isintended to refer to an example or illustration. As used herein, theterms “use,” “using,” “used”, and “approximately” may be consideredsynonymous with the terms “utilize,” “utilizing,” “utilized,” and“about” respectively.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to”, “coupled to”, or “adjacent to” anotherelement or layer, it may be directly on, connected to, coupled to, oradjacent to the other element or layer, or one or more interveningelements or layers may be present. In contrast, when an element or layeris referred to as being “directly on”, “directly connected to”,“directly coupled to”, or “immediately adjacent to” another element orlayer, there are no intervening elements or layers present.

Although exemplary embodiments of a system and method for phase noisecommon phase error and inter-carrier interference estimation andcompensation have been specifically described and illustrated herein,many modifications and variations will be apparent to those skilled inthe art. Accordingly, it is to be understood that a system and methodfor phase error and interference estimation and compensation constructedaccording to principles of the present disclosure may be embodied otherthan as specifically described herein. The present disclosure is alsodefined in the following claims, and equivalents thereof.

1-19. (canceled)
 20. A method for transmitting data in an orthogonalfrequency-division multiplexed signal including a plurality of phasetracking reference signal subcarriers, the method comprisingtransmitting the orthogonal frequency-division multiplexed signal,wherein the phase tracking reference signal subcarriers are in aplurality of subcarriers, arranged in N_(c) groups, each of the N_(c)groups comprising a plurality of adjacent subcarriers.
 21. The method ofclaim 20, wherein each group includes exactly N_(PTRS) adjacent phasetracking reference signal subcarriers, N_(PTRS) being an integer greaterthan
 0. 22. The method of claim 20, wherein a first group of the N_(c)groups includes the same number of subcarriers as a second group of theN_(c) groups.
 23. The method of claim 22, wherein a first group includesa first number of adjacent subcarriers at frequencies below thefrequencies of the phase tracking reference signal subcarriers of thefirst group and the second group includes a number, equal to the firstnumber, of adjacent subcarriers at frequencies below the frequencies ofthe phase tracking reference signal subcarriers of the second group. 24.The method of claim 20, further comprising: receiving the orthogonalfrequency-division multiplexed signal; estimating a channel usingdemodulation reference signal subcarriers from the received signal;estimating a common phase error using the estimated channel and phasetracking reference signal subcarriers from the received signal; andestimating one or more inter-carrier interference terms, including:canceling, from the received signal, the estimated common phase error toform a first compensated received signal; and estimating, based on thefirst compensated received signal, a first inter-carrier interferenceterm.
 25. The method of claim 24, further comprising calculating a valueof the transmitted signal in a subcarrier using known PTRS pilots. 26.The method of claim 24, wherein the estimating of the inter-carrierinterference terms further comprises: iteratively, for a range of valuesof an integer i greater than 1 and less than a set integer L: canceling,from the received signal, the estimated common phase error, and thefirst through (i−1)-th inter-carrier interference terms, to form an i-thcompensated received signal; and estimating, using the i-th compensatedreceived signal, an i-th inter-carrier interference term.
 27. The methodof claim 26, wherein the estimating of the common phase error comprisessetting an amplitude of the estimated common phase error to be equalto
 1. 28. The method of claim 24, wherein the phase tracking referencesignal subcarriers comprise N_(c)N_(PTRS) subcarriers, arranged in N_(c)groups, each of the N_(c) groups comprising N_(PTRS) adjacentsubcarriers, N_(PTRS) being an integer greater than 1, and N_(c) beingan integer greater than
 1. 29. The method of claim 20, furthercomprising: receiving the orthogonal frequency-division multiplexedsignal; estimating a channel using demodulation reference signalsubcarriers from the received signal; estimating a common phase errorusing the estimated channel and phase tracking reference signalsubcarriers from the received signal; and estimating one or moreinter-carrier interference terms, including: canceling, from thereceived signal, the estimated common phase error to form a firstcompensated received signal; and jointly estimating, based on the firstcompensated received signal, L inter-carrier interference terms, L beinga set integer greater than
 0. 30. The method of claim 29, furthercomprising calculating a value of the transmitted signal in a subcarrierusing known PTRS pilots.
 31. The method of claim 30, wherein theestimating of the common phase error comprises setting an amplitude ofthe common phase error to be equal to
 1. 32. The method of claim 29,wherein the phase tracking reference signal subcarriers compriseN_(c)N_(PTRS) subcarriers, arranged in N_(c) groups, each of the N_(c)groups comprising N_(PTRS) adjacent subcarriers, N_(PTRS) being aninteger greater than 1, and N_(c) being an integer greater than
 1. 33. Asystem for transmitting data in an orthogonal frequency-divisionmultiplexed signal including a plurality of phase tracking referencesignal subcarriers, the system comprising: a transmitter, thetransmitter being configured to transmit the orthogonalfrequency-division multiplexed signal, wherein the phase trackingreference signal subcarriers are in a plurality of subcarriers, arrangedin N_(c) groups, each of the N_(c) groups comprising a plurality ofadjacent subcarriers.
 34. The system of claim 33, wherein each groupincludes exactly N_(PTRS) adjacent phase tracking reference signalsubcarriers, N_(PTRS) being an integer greater than
 0. 35. The system ofclaim 33, wherein a first group of the N_(c) groups includes the samenumber of subcarriers as a second group of the N_(c) groups.
 36. Thesystem of claim 35, wherein a first group includes a first number ofadjacent subcarriers at frequencies below the frequencies of the phasetracking reference signal subcarriers of the first group and the secondgroup includes a number equal to the first number, of adjacentsubcarriers at frequencies below the frequencies of the phase trackingreference signal subcarriers of the second group.
 37. The system ofclaim 33, further comprising a receiver configured to: receive theorthogonal frequency-division multiplexed signal; estimate a channelusing demodulation reference signal subcarriers from the receivedsignal; estimate a common phase error using the estimated channel andphase tracking reference signal subcarriers; and estimate one or moreinter-carrier interference terms, including: canceling, from thereceived signal, the estimated common phase error to form a firstcompensated received signal; and estimating, based on the firstcompensated received signal, a first inter-carrier interference term.38. The system of claim 37, wherein the receiver is further configuredto calculate a value of the transmitted signal in a subcarrier usingknown PTRS pilots.
 39. The system of claim 33, further comprising areceiver configured to: receive the orthogonal frequency-divisionmultiplexed signal; estimate a channel using demodulation referencesignal subcarriers from the received signal; estimate a common phaseerror using the estimated channel and phase tracking reference signalsubcarriers; and estimate one or more inter-carrier interference terms,including: canceling, from the received signal, the estimated commonphase error to form a first compensated received signal; and jointlyestimating, based on the first compensated received signal, Linter-carrier interference terms, L being a set integer greater than 0.